"The brewer would chew grain and spit it out. As women's saliva is biologically distinct from men's saliva, it meant that the brewing process was more efficient when women brewed."

Author of A Brief History of Vice, Robert Evans, suggests that the greater concentration of enzyme amylase in women's saliva means that their beer was smoother and less sour than the man-made equivalent.

With water off-limits for many Edinburgh citizens for health and safety reasons, beer was often the alternative - and a smooth brew would certainly have been more palatable among locals.

A change in gender roles

In the 17th and 18th century the number of female brewers operating in Edinburgh decreased to nearly zero.

The sudden change was a result of the industrialisation of brewing, according to Robertson. As soon as there was money to be made, men forcibly assumed the role previously reserved for women.

"When brewing was just something you’d do to sustain yourself, the women were in charge, but when it became a business that’s when you see a big shift in the gender balance."